acl permissions: fix a bug

permsForKey sometimes returned the second longest prefix instead of the
longest one.

Change-Id: Ie67d94f1b5348b8ed0d6a35d384dcb2d79ee586e
diff --git a/services/syncbase/server/nosql/table.go b/services/syncbase/server/nosql/table.go
index 797be78..d4d07d4 100644
--- a/services/syncbase/server/nosql/table.go
+++ b/services/syncbase/server/nosql/table.go
@@ -458,8 +458,9 @@
 	if strings.HasPrefix(key, prefix) {
 		return prefix, prefixPerms, nil
 	}
+	parent := prefixPerms.Parent
 	prefixPerms, err := t.permsForPrefix(ctx, sntx, prefixPerms.Parent)
-	return prefixPerms.Parent, prefixPerms, err
+	return parent, prefixPerms, err
 }
 
 // permsForPrefix returns the permissions object associated with the